Next Danger: "Splash Crash"

Markets are ill-prepared for a high-speed trading disruption that might simultaneously affect stocks, commodities, bonds and other assets.

Last year's Flash Crash was a hair-raising experience for stock and commodities investors—comparable to the sudden descent of a large airliner from 38,000 feet to tree-top level, followed by an equally sudden and steep ascent.

A trillion dollars in equity vanished in minutes, as stock futures, exchange-traded funds and equities plunged. I've recently heard from a computer-trading expert warning of the very real possibility of a more widespread and catastrophic "splash crash," a dislocation by high-speed trading...